<b>Rapid, Multi-Sample Assay of Gabapentin in Capsules Using Easy-to-Setup and Low-Cost Smartphone-Based Fluorescence Measurement</b>

Background: Pharmacopeial methods for the quantification of gabapentin (GBP), particularly high-performance liquid chromatography (HPLC), require costly instrumentation, unsafe solvents in mobile phase, and time-consuming procedures. While fluorometric methods exist, they also employ expensive fluorometers. This study aimed to develop a cost-effective, eco-friendly GBP assay using smartphone-based digital image fluorometry (SDIF) for rapid multi-sample analysis of GBP in pharmaceutical capsules. Methods: GBP was reacted with fluorescamine in borate buffer (pH 9.0) for 2 minutes, producing a blue fluorescent product under UV light. Fluorescence intensity was captured using a smartphone inside a dark box with low-cost UV LEDs (395 nm). GBP concentration was determined from green (G) channel intensity using a logarithmic calibration curve. The method was optimized, validated per USP guidelines, and compared with USP HPLC. Greenness and practicality were evaluated. Results: The SDIF method exhibited excellent linearity (r² = 0.9994) over GBP concentrations of 0.2–4.0 μg/mL, with high accuracy (98%–102% recovery) and precision (RSD &lt; 2%). No interference was observed from capsule excipients or the impurity GBP-related compound A. Assay results showed no significant difference from the USP HPLC method. Compared to HPLC, the SDIF method demonstrated a greener profile by using acetone instead of acetonitrile. Although requiring derivatization and offering lower automation than HPLC, SDIF achieved a satisfactory Blue Applicability Grade Index (BAGI) score of 65.0, indicating practical applicability. Additionally, the method allowed simultaneous measurement of six samples and six standard solutions, unlike HPLC or fluorometers, which measure only one at a time. Conclusion: SDIF eliminates the need for fluorometers or HPLC, using inexpensive and simple equipment for rapid, multi-sample GBP analysis. With its green profile and practicality, SDIF offers a viable alternative for routine quality control, particularly in resource-limited settings.